SQL HAVING 子句

HAVING 子句使你能夠指定過濾條件，從而控制查詢結果中哪些組可以出現在最終結果里面。

WHERE 子句對被選擇的列施加條件，而 HAVING 子句則對 GROUP BY 子句所產生的組施加條件。

語法：

下面可以看到 HAVING 子句在 SELECT 查詢中的位置：

SELECT
FROM
WHERE
GROUP BY
HAVING
ORDER BY

在 SELECT 查詢中，HAVING 子句必須緊隨 GROUP BY 子句，并出現在 ORDER BY 子句（如果有的話）之前。帶有 HAVING 子句的 SELECT 語句的語法如下所示：

SELECT column1, column2
FROM table1, table2
WHERE [ conditions ]
GROUP BY column1, column2
HAVING [ conditions ]
ORDER BY column1, column2

示例：

考慮 CUSTOMERS 表，表中的記錄如下所示：

+----+----------+-----+-----------+----------+
| ID | NAME     | AGE | ADDRESS   | SALARY   |
+----+----------+-----+-----------+----------+
|  1 | Ramesh   |  32 | Ahmedabad |  2000.00 |
|  2 | Khilan   |  25 | Delhi     |  1500.00 |
|  3 | kaushik  |  23 | Kota      |  2000.00 |
|  4 | Chaitali |  25 | Mumbai    |  6500.00 |
|  5 | Hardik   |  27 | Bhopal    |  8500.00 |
|  6 | Komal    |  22 | MP        |  4500.00 |
|  7 | Muffy    |  24 | Indore    | 10000.00 |
+----+----------+-----+-----------+----------+

下面是一個有關 HAVING 子句使用的實例，該實例將會篩選出出現次數大于或等于 2 的所有記錄。

SQL > SELECT ID, NAME, AGE, ADDRESS, SALARY
FROM CUSTOMERS
GROUP BY age
HAVING COUNT(age) >= 2;

其執行結果如下所示：

+----+--------+-----+---------+---------+
| ID | NAME   | AGE | ADDRESS | SALARY  |
+----+--------+-----+---------+---------+
|  2 | Khilan |  25 | Delhi   | 1500.00 |
+----+--------+-----+---------+---------+